A survivor's guide to keeping warm in the cold

Ever wonder if you really lose most of your heat through your head? Or if a hot bowl of chicken noodle soup will warm your innards on a cold day?

HOWARD FRANK

Ever wonder if you really lose most of your heat through your head? Or if a hot bowl of chicken noodle soup will warm your innards on a cold day?

We've talked to an expert on staying warm through the winter, and here's what he said.

Keeping warm in the cold is simply a matter of preventing heat loss, according to Professor David Avreril of the Commonwealth Medical College in Scranton. He teaches physiology to first-year medical students.

Your body is a heat producer — the heat is a byproduct from various metabolic processes in our bodies. We eat stuff and burn it up. That generates heat, Avreril said.

But to prevent heat loss, we first must understand how we lose heat.

Our bodies constantly transfer heat to the environment around us through a temperature gradient — the difference between our body's temperature and our immediate surroundings. If the air around us is colder, we lose heat to the air until the air and our bodies are the same temperature.

We lose heat in four ways.

First, we radiate heat. It's the transfer of heat in the form of electromagnetic energy. Think of the sun's rays traveling invisibly from space to your lounge chair by the pool. Your body loses heat the same way, by radiating it. Block the waves and you'll stop the heat loss.

Radiation heat transfer is the most common way our body loses heat. The best way to prevent it is to cover up, insulate yourself and keep those waves from escaping your body.

The second way we lose heat is through conduction — by having physical contact with another body. An example is sitting on a rock that feels cold. Again, temperature gradient heat moves from the warm body to the colder rock.

The amount of heat transfer is a function of the surface area between the body and the rock. The bigger the rock surface that contacts your body, the greater your heat loss.

Convection heat transfer is the third way we lose heat, and this is important.

Remember, our bodies lose heat to the surrounding cool air by warming it and narrowing the gradient between us and the air.

Now, imagine the wind is blowing, and the air your body just warmed is constantly being blown away and replaced with new, unheated air. The gradient increases again and you feel colder. This is what's known as the wind chill factor. Your body loses even more heat.

The final process is evaporative heat transfer. It's when we lose heat from within our body as it converts water to water vapor. That takes a lot of energy, Avreril said. But it's a particularly good way to cool the body down.

One example is sweating. But in the winter, we lose heat by producing water vapor in another way — by talking.

"When we breathe, we actually lose some heat because some of the water in our airways can be converted to a gas," Avreril said. "So every time we breathe, we lose heat."

Cover your mouth in the cold and exhale and you'll know what we mean. Losing heat through breathing isn't a good way for people to cool down, but it's very effective for dogs since they can't lose heat through their fur.

So, how do we stay warm while we are walking from our car to the mall?

Increasing the insulation around you reduces the amount of heat we lose through radiation, conduction and convection, Avreril said. That's why having a good coat is really important.

Do we really lose most of our heat through our heads?

Yes and no.

The head is no different than any other body part, and remember: The heat loss is a function of the exposed surface area.

But what do we do when we go out in the cold? We put on a jacket. Yet we often leave our heads bare, therefore causing our greatest heat loss.

It's no different than if you forgot your gloves, although the hands involve a lot less surface area, and therefore less heat loss.

So what's the good professor's best advice for staying warm during these frigid winter months?

"Don't go out when it's really cold and windy," he said.

Why didn't we think of that?

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